Data storage devices often use magnetic recording to store data on magnetic media. For instance, a disk drive includes a transducer head and a magnetic disk. The transducer head includes a read element that magnetically reads data from the disk and a write element that magnetically records (writes) data on the disk. The disk is magnetic media that stores the data in concentric tracks.
In longitudinal recording, data is stored on the disk in horizontal transitions (bits) that are parallel to the disk. In perpendicular recording, data is stored on the disk in vertical transitions (bits) that are perpendicular to the disk. Perpendicular recording allows for greater data storage than longitudinal recording since data stored at high areal density degrades less over time in perpendicular recording than in longitudinal recording.
In perpendicular recording, the write element includes a large pole and a small pole, and the large pole has larger dimensions than the small pole. The disk includes a soft underlayer that collects the magnetic field from a large area and couples the magnetic field to the large pole. As a result, the transducer head is biased during write operations due to the magnetic field from other tracks being coupled to the large pole. The bubble, where data is written to the disk, either expands or contracts due to the magnetic field.
Disk preconditioning plays a major role in disk drive performance. Disk preconditioning involves demagnetizing (erasing) the disk before data is recorded on the disk. Disk drive performance includes bit error rate (BER) represented by the number of bits in error read from the disk in a readback signal divided by the number of bits read from the disk in the readback signal.
DC erase applies an essentially constant current to the write element to demagnetize the disk. DC erase is typically applied to disk areas for servo wedges and user data before data is recorded on the disk. Thereafter, data such as servo patterns and user data is initially recorded on the disk.
DC erase in longitudinal recording has negligible effects since the disk lacks a soft underlayer. However, in perpendicular recording, DC erase increases the BER in the readback signal from the recorded data by up to two orders of magnitude since the soft underlayer couples the magnetic field from the DC erased area to the write element as the data is written to the disk. The magnetic coupling enhances one polarity of the writing and degrades the other such that the positive or negative bit cells last longer than the other. Thus, the magnetic coupling causes transition shift on the disk. The transition shift creates timing asymmetry during read operations, and the timing asymmetry degrades the BER. As a result, the DC erase has a large negative impact on disk drive performance.
There is, therefore, a need for an improved technique for demagnetizing the magnetic media for a data storage device that reduces or eliminates the effect of the adjacent magnetic field on the data that is subsequently written to the magnetic media.